Aims: 

Astrocytes constitute the brain cell population the most widely coupled by gap junctions that organize these cells as multicellular networks. Indeed, intercellular channels made by connexins provide direct cell-to-cell communication allowing astrocytes to work as groups of communicating cells rather than independent units. How are organized such astrocytic networks and what are the rules that govern their shape and function constitute critical questions to understand their interaction with neuronal circuitry.

Methods: 

Gap junctional communication (GJC) was investigated by patch-clamp recording and dye-coupling in acute brain slices while the distribution of the two astrocytic connexins was assessed by immunohistochemistry and confocal microscopy.

Results: 

In the somatosensory cortex, where layer IV neurons constitute anatomo-functional compartments, connexin expression is enriched in the barrels, while GJC is restricted in the barrel-to-barrel axis and favoured toward their center. In the CA1 region of the hippocampus, the extent of GJC is controlled by glutamate released from neurons in an activity-dependent manner and by bioactive peptides. The use of fluorescent glucose derivatives demonstrated that GJC allows intercellular trafficking of energetic compounds and rescues neuronal activity following glucose deprivation.

Conclusion: 

Astrocytes are organized as communicating networks tightly regulated by neurons. The shaping of astrocytic networks depends on the local organization of neurons and on their activity indicating that they are dynamically controlled. Finally, the permeability properties of gap junction channels in astrocytes provide a basis for their contribution to the metabolic supply by glia to neuronal activity.